André Villas-Boas has urged the Tottenham Hotspur board to invest strongly in the squad over the summer in order for them to close the gap to the Premier League's top four, after they narrowly failed to reach the level this season.

The disappointment was etched into Villas-Boas's features and, although there was fury from Paolo Di Canio, who launched into an extraordinary tirade about the indiscipline in his Sunderland squad, Tottenham's manager sought to look to next season when, he predicted, all of the top four, plus Liverpool, will strengthen significantly.

"We had to be aware, independent of making it or not – and we didn't make it – that we would have to raise the bar again because our competitors will do the same," Villas-Boas said. "They will do their job in window and we must do ours, in the Tottenham way, scouting properly and looking for good grabs in summer window to make it a stronger squad."

Only once since the Premier League slimmed down to 20 clubs in 1995-96 has the team in fourth taken more than 72 points – Liverpool finished with 76 in 2007-08 – and Villas-Boas spoke of Tottenham's tally being a "reference point" for next season.

He congratulated Arsenal for their outstanding burst of form since they lost at White Hart Lane on 3 March and he said that Tottenham's defeats by Liverpool and Fulham after that derby had proved hurtful. But he described the one at Everton last December as "the game that cost us most". Tottenham had led 1-0 going into the last minute.

Villas-Boas's regrets on the final day were linked to the referee, Andre Marriner, principally in his decisions to turn down two strong Tottenham penalty appeals – one for an apparent foul by Sebastian Larsson on Bale in the early going and the other for handball against Carlos Cuéllar in the second half. Marriner, who had visited Tottenham's training ground last December to advise Bale over his bookings for diving, cautioned him for simulation. TV replays showed there had been contact.

"I think it [the first penalty appeal] would have been absolutely decisive," Villas-Boas said. "We would obviously have to score it but it would certainly have been felt at Newcastle. It was extremely disappointing, as Andre was in the meeting earlier in the season."